using System; using System.Text.RegularExpressions; using System.Net;  

using System.Web; using System.Text;

public static class Program

{

    //Tue 20-Aug-19 6:53pm Markus - http://metadataconsulting.blogspot.com/2019/08/Remove-all-ANSI-Control-Characters-fast-in-C-Sharp.html

    public static string RemoveUnicodeControlChars(this string s) {

        StringBuilder sb = new StringBuilder(s.Length);

        for (int i = 0; i < s.Length; i++) 

        if ( !Char.IsControl(s[i]) )

            sb.Append(s[i]);

        return sb.ToString(); 

    }

    public static string URLExpander(this string URL) {

            //removal ASCII and UNICODE control characters, if they exist

            //string urlText = Regex.Replace(URL, @"[\u0000-\u0008|\u000B-\u000C|\u000E-\u001F|\u0080-\u009F]", "");

            string urlText = URL.RemoveUnicodeControlChars(); 

            if (string.IsNullOrWhiteSpace(urlText))

                return string.Empty; 

​

            Uri uriResult;

​

            //validate URL

            bool result = Uri.TryCreate(urlText, UriKind.Absolute, out uriResult)

            && (uriResult.Scheme == Uri.UriSchemeHttp || uriResult.Scheme == Uri.UriSchemeHttps

                || uriResult.Scheme == Uri.UriSchemeFtp || uriResult.Scheme == Uri.UriSchemeFile

                ); //or other schemes

​

            if (!result)

                return string.Empty;

​

            //https://docs.microsoft.com/en-us/dotnet/api/system.net.httpwebrequest?view=netframework-4.8

            HttpWebRequest req = null; 

            HttpWebResponse response; 

            try

            {

                req = (HttpWebRequest)WebRequest.Create(uriResult); 

                req.Method = "HEAD";

                req.AllowAutoRedirect = false;

                result = true; 

            }

            catch (NotSupportedException)

            {

                result = false; //add your exception handling here

            }

            catch (ArgumentNullException)

            {

                result = false; //add your exception handling here

​

            }

            catch (System.Security.SecurityException)

            {

                result = false; //add your exception handling here

​

            }

            catch (UriFormatException)

            {

                result = false; //add your exception handling here

            }

​

            if (!result)

                return string.Empty; 

            string redirectedURL = ""; 

            try

            {

                response =  (HttpWebResponse)req.GetResponse();

                //https://en.wikipedia.org/wiki/List_of_HTTP_status_codes

                //304 Not Modified - Redirection to a previously cached result -> may not be a URL redirection

                //restrictive

                if ((int)response.StatusCode >= 300 && ((int)response.StatusCode < 400))

                {

                    redirectedURL = response.Headers[HttpResponseHeader.Location]; //or url = response.Headers["Location"];

                }

                else if ((int)response.StatusCode < 300 || (int)response.StatusCode >= 400) //okay

                {

                    redirectedURL = uriResult.ToString(); //set as validated URL

                }                               

​

                result = true; 

            }       

            catch (System.Net.WebException)

            {

                result = false; 

            }

            catch (System.Net.ProtocolViolationException)

            {

                result = false; 

            }

            catch (InvalidOperationException)

            {

                result = false;                 

            }

            catch (NotSupportedException)

            {

                result = false; 

            }

            if (!result)

                return string.Empty;

            try {

                redirectedURL = HttpUtility.UrlDecode(redirectedURL);

            }

            catch 

            {

                return string.Empty; 

            }

            return redirectedURL; 

    }

    public static void Main()

    {

        string testURL = "http://bit.ly/AzureAITranslation"; 

        string testURL2 = "https://metadataconsulting.blogspot.com"; 

            //sanity check - no redirect especially for status code 304 (which is cached URL)

        string expandoURL = testURL.URLExpander(); 

        if (testURL == expandoURL)

            Console.WriteLine("source URL same as output URL");

        else if (testURL + "/" == expandoURL) 

            Console.WriteLine("source URL same as output URL");

        else

            Console.WriteLine("source URL expands to new URL");

        Console.WriteLine(testURL + "\nexpands to\n" + testURL.URLExpander());

        Console.WriteLine(); 

        expandoURL = testURL2.URLExpander(); 

        if (testURL2 == expandoURL)

            Console.WriteLine("source URL same as output URL");

        else if (testURL2 + "/" == expandoURL) 

            Console.WriteLine("source URL same as output URL");

        else

            Console.WriteLine("source URL expands to new URL");

        Console.WriteLine(testURL2 + "\nexpands to\n" + testURL2.URLExpander());

​

​

    }

}